Separation methods for water treatment include a method using a filtering membrane, a method using heat or phase-change, and so on.
A separation method using a filtering membrane has a lot of advantages over the method using heat or phase-change. Among the advantages is the high reliability of water treatment since the water of desired purity can be easily and stably obtained by adjusting the size of the pores of the filtering membrane. Furthermore, since the separation method using a filtering membrane does not require a heating process, the method can be used together with microorganisms which are useful for separation process but might be adversely affected by heat.
Among the separation methods using a filtering membrane is a method using a hollow fiber membrane. Typically, a hollow fiber membrane has been widely used in the field of microfiltration and/or ultrafiltration for obtaining axenic water, drinking water, super pure water, and so on. Recently, the application of the hollow fiber membrane is extended to wastewater treatment, solid-liquid separation in a septic tank, removal of suspended solid (SS) from industrial wastewater, filtration of river, filtration of industrial water, filtration of swimming pool water, and the like.
As the water treatment process is performed by the filtering membrane module, the impurities existing in the feed water causes the fouling problem, i.e., the contamination of the filtration membrane, which reduces the filtration efficiency of the filtering membrane. Since the contaminants of various forms causes the membrane contamination in various ways, it is required to clean the contaminated filtering membrane in various manners. The cleaning of the contaminated filtering membrane may be classified into a maintenance cleaning and a recovery cleaning in accordance with the purpose of the cleaning.
The recovery cleaning is a cleaning performed for relatively long time when serious deterioration in membrane permeation performance is caused to the filtering membrane module due to the contaminants accumulated as the water treatment is performed for a long time. The main purpose of the recovery cleaning is to recover the permeation performance of the filtering membrane.
On the other hand, the maintenance cleaning is a cleaning performed during the filtering process or while the filtering process is stopped for relatively short time. The main purpose of the maintenance cleaning is to maintain the permeation performance of the filtering membrane in a good state. The maintenance cleaning is mainly performed through a physical cleaning. The physical cleaning may be classified into a backwashing cleaning and an aeration cleaning.
The backwashing cleaning is a cleaning performed by causing the air or water to flow backward through the filtering membrane during a temporary stoppage of the water treatment, thereby removing the impurities adhered to the surface of the membrane. On the other hand, according to the aeration cleaning, the air is jetted from the aeration tubes to create the bubbles moving upwardly within the feed water (contained in the water treatment tank or housing). The impurities adhered to the surface of the filtering membrane are removed not only by the rising bubbles themselves but also by the ascending flow or circulation of the feed water which is created by the rising bubbles.
A submerged-type filtering apparatus which performs the filtration process while submerged in the feed water to be treated typically comprises a frame structure and a filtering membrane module installed therein. Since the air is strongly jetted from the aeration tubes during the aeration cleaning, if the filtering membrane module is coupled to the frame structure loosely, the filtering membrane module suffers severe relative vibration within the frame structure.
As a result of that, the filtering membrane module gets damaged while colliding with the frame structure, which causes serious problems in that the replacement cycle of the filtering membrane module is shortened and the cost for the replacement increases.
What is more serious is that, if the relative vibration of the filtering membrane module within the frame structure continues to cause their connection to be more loose or cause the filtering membrane module itself to be damaged, the filtering membrane module will be separated from the frame structure and the non-treated feed water will be introduced to the permeate storage tank.
A submerged-type filtering apparatus is disclosed in Korean Laid-Open Patent Publication No. 10-2009-0043638 (hereinafter, ‘prior art’) published on May 7, 2009.
The filtering apparatus of the prior art comprises a frame structure having overall shape of cuboid and hollow fiber membrane modules installed therein. The frame structure comprises four vertical members and four cross bars supported by the vertical members respectively, and the hollow fiber membrane module comprises two headers and hollow fiber membranes therebetween.
According to the prior art, a coupling ring is formed on the header of the hollow fiber membrane module, and an elastic coupling member is combined to the front cross bar of the frame structure. The elastic coupling member comprises a pair of elastic wings and protrusions formed on the outer sides of the elastic wings.
When the hollow fiber membrane module is installed in the frame structure, the pair of elastic wings pass through the hole of the coupling ring of the header. When the protrusions respectively formed on the outer sides of the elastic wings are passing through the hole of the coupling ring, the pair of elastic wings get bent in such a manner that they become closer to each other. Then, the elastic force makes the pair of elastic wings come back to the original position right after the protrusions of the elastic coupling member pass through the hole of the coupling ring. Once the installation of the hollow fiber membrane module in the frame structure is completed, the protrusions prevent the elastic coupling member from getting out of the hole of the coupling ring.
However, according to the aforementioned structure, the pair of coupling wings to be inserted into the coupling ring of the header must have elasticity, and thus the relative vibration of the hollow fiber membrane module within the frame structure cannot be inhibited completely. Furthermore, since the coupling state of the frame structure and hollow fiber membrane module depends only on the small protrusions, there is a high risk that the protrusions are damaged due to the relative vibration of the hollow fiber membrane module, thereby causing the hollow fiber membrane module to be separated from the frame structure.